Raman Emission Research Articles

Solid state solvation: a fresh view.

The design of efficient organic electronic devices, including OLEDs, OPVs, luminescent solar concentrators, etc., relies on the optimization of relevant materials, often constituted by an active (functional) dye embedded in a matrix. Understanding solid state solvation (SSS), i.e. how the properties of the active dye are affected by the matrix, is therefore an issue of fundamental and technological relevance. Here an extensive experimental and theoretical investigation is presented shedding light on this, somewhat controversial, topic. The spectral properties of the dye at equilibrium, i.e. absorption and Raman spectra, are not affected by the matrix dynamics. Reliable estimates of the matrix polarity are then obtained from an analysis of the micro-Raman spectra of polar dyes. Specifically, to establish a reliable polarity scale, the spectra of DCM or NR dispersed in amorphous matrices are compared with the spectra of the same dyes in liquid solvents with known polarity. On the other hand, steady-state emission spectra obtained in solid matrices depend in a highly non-trivial way on the matrix polarity and its dynamics. An extensive experimental and theoretical analysis of the time-resolved emission spectra of NR in a very large time window (15 fs-15 ns) allows us to validate this dye as a good probe of the dielectric dynamics of the surrounding medium. We provide a first assessment of the relaxation dynamics of two matrices (mCBPCN and DPEPO) of interest for OLED application, unambiguously demonstrating that the matrix readjusts for at least 15 ns after the dye photoexcitation.

Development of a near-infrared Raman spectroscopy setup compatible with fluorescence-guided surgery.

Near-infrared (NIR) fluorescence imaging using exogenous fluorescent agents provides whole-field images in real-time to assist the surgeon in the excision of a tumor. Although the method has high sensitivity, the specificity can sometimes be lower than expected. Raman spectroscopy can detect tumors with high specificity. Therefore, a combination of both techniques can be advantageous. A complication that must be addressed is that the NIR spectral region is favored by both techniques for (in vivo) tissue analysis. When fluorescence and Raman emissions spectrally overlap, it becomes challenging or impossible to detect the Raman signal. In this paper, by avoiding this overlap, we describe a Raman spectroscopy setup capable of recording high-quality Raman spectra from tissue containing NIR exogenous fluorescent agents. We identify an optimal wavelength interval (900-915 nm) for Raman excitation, which avoids both excitation of fluorescent dyes and Raman signal self-absorption by the tissue. In this way, Raman spectroscopy can be combined with the currently most-used NIR fluorescent dyes. This combined novel setup could pave the way for clinical trials benefiting from both fluorescence imaging and Raman spectroscopy to avoid positive margins in cancer surgery.

Laser-transmission-induced Raman emission masked by progressive transparency in polymer waveguides.

Laser-transmission-induced Raman emission (LTIR) in polymer waveguides is observed and analyzed in this work. When injected with a 532-nm continuous-wave laser of 10 mW, the waveguide shows a distinct line of orange-to-red emission, which is quickly masked by the green light in the waveguide due to the laser-transmission-induced transparency (LTIT) at the source wavelength. However, when a filter is applied to remove the emission below 600 nm, a clear red line is shown in the waveguide, which stays constant over time. Detailed spectral measurements show that the polymer material can generate broadband fluorescence when illuminated with the 532-nm laser. However, a distinct Raman peak at 632 nm only appears when the laser is injected into the waveguide with much higher intensity. The LTIT effect is fitted based on experimental data to describe the generation and fast masking of the inherent fluorescence and LTIR effect empirically. The principle is analyzed through the material compositions. This discovery may trigger novel on-chip wavelength-converting devices using low-cost polymer materials and compact waveguide structures.

Time Resolved Raman Scattering of Molecules: A Quantum Mechanics Approach with Stochastic Schroedinger Equation.

Raman scattering is a very powerful tool employed to characterize molecular systems. Here we propose a novel theoretical strategy to calculate the Raman cross-section in time domain, by computing the cumulative Raman signal emitted during the molecular evolution in time. Our model is based on a numerical propagation of the vibronic wave function under the effect of a light pulse of arbitrary shape. This approach can therefore tackle a variety of experimental setups. Both resonance and nonresonance Raman scattering can be retrieved, and also the time-dependent fluorescence emission is computed. The model has been applied to porphyrin considering both resonance and nonresonance conditions and varying the incident field duration. Moreover the effect of the vibrational relaxation, which should be taken into account when its time scale is similar to that of the Raman emission, has been included through the stochastic Schroedinger equation approach.

Laser Guide Star uplink beam: scattering and Raman emission measurements with the 10.4m Gran Telescopio CANARIAS

ABSTRACT Laser Guide Star Adaptive Optics (LGS-AO) is becoming routine in several astronomical observatories. The use of powerful lasers generates sensible Raman emissions on the uplink laser beam path, plus secondary Rayleigh scattering from atmospheric molecules and Mie scattering from aerosols. This paper reports the results of a campaign done with the 10.4m Gran Telescopio CANARIAS (GTC); this campaign was undertaken to assess the spectral and photometric contamination coming from a 589 nm laser uplink beam scattering and Raman emission induced on the GTC spectro-imager OSIRIS by laser launched ∼1 km off-axis. The photometric contamination is due to primary and secondary scattering of the uplink photons, as well by the Raman inelastic scattering. We have propagated the laser beam creating a mesospheric LGS, then pointed and focused the GTC telescope towards the uplink laser beam, at different heights and up to the LGS, taking into account the observing geometry. In our observations, the Raman emissions for O2 and N2 vibrational lines are visible at 20 km, weakening with altitude and becoming undetectable above 30 km. The scattering of the focused uplink beam is detectable at less than ±0.2 arcmin from the centre of the beam, while for the focused LGS the scattering is narrower, being detectable at less than ±0.1 arcmin around the plume. Recommendations for Laser Traffic Control Systems are given accordingly.

Raman lasing and other nonlinear effects based on ultrahigh-QCaF2 optical resonator

The calcium fluoride (CaF2) whispering gallery mode crystalline resonator is an excellent platform for nonlinear optical applications because of the decreasing in threshold caused by ultrahigh quality (Q) factor. In this paper, we achieved the observation of Raman lasing, first-order Raman comb, and second-order Raman lasing in a CaF2 disk resonator with a diameter of 4.96 mm and an ultrahigh-Q of 8.43×108 at 1550-nm wavelength. We also observed thermal effects in CaF2 disk resonator, and the threshold of thermo-optical oscillation is approximately coincident with Raman lasing, since the intracavity power increases rapidly when the power reaches the threshold, and higher input pump power results in longer thermal drift and higher Raman emission power. With a further increase in pump power, the optical frequency combs range is from 1520 nm to 1650 nm, with a wavelength interval of 4×FSR. It is a promising candidate for optical communication, biological environment monitoring, spectral analysis, and microwave signal sources.

Simple design of Yb-doped fiber laser with an output power of 2 kW

We report a simple design of Yb-doped fiber laser providing a record output power of 2kW and power conversion efficiency of 68%. The high output power of this unamplified laser oscillator is obtained thanks to the suppression of Raman emission over a spectral range of 21 nm from chirped and tilted fiber Bragg gratings inside the gain fiber of the laser oscillator. The laser design is based on optical components that are commercially widespread and low-cost, such as 20μm-core double-cladding active and passive fibers, as well as pump laser diodes at a wavelength of 915 nm. The performance of this laser is evaluated in terms of output power, power conversion efficiency, and thermal dissipation. A numerical model that serves to determine the optimal experimental configuration is also provided.

Structural, vibrational and luminescence properties of solid solution based on the (1-x/2) Ce2(WO4)3 + (x/2) Sm2(WO4)3 system

A series of 14 polycrystalline cerium samarium tungstates belonging to the system [(1-x/2).Ce2(WO4)3 + x/2 Sm2(WO4)3] was synthesized by a coprecipitation method followed by thermal treatment at 1000 °C. The polycrystalline samples were characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. Their crystal structure was subjected to Rietveld refinement calculations and quasi-linear variation of cell parameters was observed, suggesting the formation of a solid solution Ce(2-x)Smx(WO4)3 (0 ≤ x ≤ 2). Raman spectroscopy was used to confirm the formation of the disordered solid solution. The analyses of Bragg peak and Raman emission profiles allowed evidencing the formation of structural defects. Scanning electron microscopy images show relatively well crystallized grains. Photoluminescence experiments were performed under polychromatic X-ray excitation delivered by copper source. The characteristic luminescence of Ce3+ cations was not observed whatever the composition x. The resulting emissions were ascribed to Sm3+ cations associated with additional emission from structural defects. Chromaticity diagrams show that color coordinates vary with Sm composition and structural defects in the orange-red range.

Raman and glow discharge optical emission spectroscopy studies on structure and anion incorporation properties of a hydrated alumina film on aluminum

Hydration treatment of aluminum in hot water is important for its corrosion protection, and also this treatment is a crucial pretreatment in forming dielectric crystalline alumina films on the aluminum anode in aluminum electrolytic capacitors. In this study, a two-layer hydrated film formed on high purity aluminum by hot water treatment was examined using a combination of glow discharge (GD) sputtering and Raman spectroscopy. In addition, the anion penetration behavior through the hydrated alumina layer during anodizing aluminum in several electrolytes was investigated. The results indicate that the outer layer, with a nanosheet-like morphology, consists of a crystalline pseudo-boehmite phase, whereas the relatively compact inner layer is amorphous or poorly crystalline. The inner amorphous layer plays a crucial role in the incorporation of the anions, which is found for the first time. When hydrated aluminum is anodized in phosphate, silicate, and tungstate electrolytes, the inner hydrated alumina layer impedes the penetration of these electrolyte anion species. In contrast, boron species readily penetrate the hydrated alumina layer into the barrier layer formed by anodization in boric acid. This anion-specific incorporation behavior is discussed in terms of ion-selective permeation in the amorphous hydrated alumina layer.

Study of Exfoliated Molybdenum Disulfide (MoS2)

In this study, We demonstrate mono and few layers MoS2 samples on the SiO2 (270nm)/Si substrate from bulk MoS2 crystal by micromechanical exfoliation technique. We also report that the Raman and PL intensity can be thermally modulated by annealing 1L, 2L and 7LMoS2 in a vacuum or air. We have systematically studied Atomic Force Microscopy, Raman and PL properties of mono and few layer MoS2 on the SiO2 (270nm)/Si substrate. First, we find that the number of layer values dependent the Raman and PL emission. First, Raman intensity area ratio of the MoS2 E12g, Ag1 and 2LA modes to that area of the Si substrate increased linear with increasing number of layers MoS2. Second, Normalized PL intensity area of the (A) peak decreased linear with increasing number of layers MoS2. The value of those graphs is a method to understand the number of layers the exfoliated MoS2. Third we found that some effects of the few layers MoS2after thermal annealed (vacuum and air 3000C for 40 min).

Monodispersed silver-gold nanorods controllable etching for ultrasensitive SERS detection of hydrogen peroxide-involved metabolites

Hydrogen peroxide (H2O2)-involved metabolites are widely engaged in cellular metabolism, and play significant roles in cell proliferation, cell growth, and signaling transduction. It is highly desirable to establish a method for the detection of H2O2-involved metabolites for applications ranging from chemical sensing to biomedical diagnosis. Herein, monodispersed sandwich Au@4-MBN@Ag@PEG nanorods (referred to as AMPRs) with bright Raman emission were developed to serve as a universal platform for detecting H2O2-involved metabolites (4-mercaptobenzonitrile is abbreviated to 4-MBN as the Raman reporter and PEG is polyethylene glycol). The system detects metabolites through changes in the surface-enhanced Raman scattering (SERS) spectrum, resulting from the controllable etching of the silver layer by the H2O2 produced by the metabolites. The integrative nanoplatform was successfully used to quantify the levels of glucose, lactate, and choline in aqueous solutions by exploiting the close linear relationship between the intensity of a SERS band and the logarithmic concentration of H2O2. The presented SERS nanoplatform demonstrated considerable practicability for the detection of glucose in cerebrospinal fluid samples (with a limit of detection (LOD) of 1.76 μM), and was capable of distinguishing infected from uninfected individuals. Therefore, the SERS sensor provides a new platform for the detection of H2O2-involved metabolites in biological fluids, and has potential for use in metabolite analysis and biomedical diagnostics.

A Combined Spectroscopic and Theoretical Study on a Ruthenium Complex Featuring a π-Extended dppz Ligand for Light-Driven Accumulation of Multiple Reducing Equivalents.

The design of photoactive systems capable of storing and relaying multiple electrons is highly demanded in the field of artificial photosynthesis, where transformations of interest rely on multielectronic redox processes. The photophysical properties of the ruthenium photosensitizer [(bpy)2Ru(oxim‐dppqp)]2+ (Ru), storing two electrons coupled to two protons on the π‐extended oxim‐dppqp ligand under light‐driven conditions, are investigated by means of excitation wavelength‐dependent resonance Raman and transient absorption spectroscopies, in combination with time‐dependent density functional theory; the results are discussed in comparison to the parent [(bpy)2Ru(dppz)]2+ and [(bpy)2Ru(oxo‐dppqp)]2+ complexes. In addition, this study provides in‐depth insights on the impact of protonation or of accumulation of multiple reducing equivalents on the reactive excited states.

Boron Induced Crystallization of Silicon on Glass: an Alternate Way to Crystallize Amorphous Silicon Films for Solar Cells

Demand for efficient window layer in thin film solar cells with high crystallinity is ever increasing that finds important application in multi-junction/tandem silicon solar cells. Doping of diborane (B2H6) in hydrogenated silicon films using plasma discharge decomposition of silane (SiH4) and (B2H6) gases were analyzed. The boron flow (FB) to silane ratio was varied from 0 to 0.30. Variation in film characteristics with B2H6 gas-phase ratio were analyzed, and concluded that doping boron induces crystallization in hydrogenated amorphous silicon (a-Si: H) film structure. The Raman and field emission scanning electron spectroscopy (FESEM) confirmed the boron induced crystallinity effect in silicon films at different diborane flow. The results showed that as boron content increases beyond certain ratio, silicon crystallization suppresses and the crystallite sizes were also reduced. From results, it was observed that crystallinity in FB = 0.05 is 79% and decreases to 77% when films are slightly higher doped (FB = 0.10) and further decreases when the films were heavily doped. These results validate that boron suppresses silicon crystallization due to local deformations caused by the impurities. Infra-red absorption studies and their analysis also confirm the crystallization in boron doped films with additional band appears at ~ 611 cm−1. This band is named as boron induced crystallinity mode of vibrational spectra. The estimated hydrogen content (CH) decreases confirmed crystallinity in the silicon structure with boron doping. Further, the energy dispersive spectroscopy (EDX) indicates the presence of boron and other impurities in deposited silicon films. The effect of boron on crystallinity and crystallite size as well as the mechanism were presented in detailed.

Using molecular marking in security holograms

Subject of study. The capabilities of the technologies for marking products and security holograms based on the analysis of the spectral properties of molecular structures introduced to the holograms are considered in combination with the adoption of quantum dots and magnetic microparticles (MPs). The primary focus is on the issues of the analysis of the Raman spectra of molecules excited by plasmonic-resonant electromagnetic fields. Method. Modern technologies for hologram security are based on the use of various protective optical effects concealed from visual observation. These effects reveal themselves only under the relevant illumination of holograms when specialized optical equipment is employed. Unique methods for marking and identification of holograms using the magneto-optical, fluorescent, and spectral properties of the emission of MPs and molecular structures with sizes ranging from tens of nanometers to tens of micrometers, which are excited by localized electromagnetic fields, are considered. The plasmonic-resonant methods for the excitation of marking molecular labels introduced into the hologram structures are the most relevant, together with the arising spectra of surface-enhanced Raman scattering that are used for the identification and authenticity verification of the holograms. Main results. The use of plasmonic-resonant methods for concentrating electromagnetic fields for the excitation of marking molecular labels was demonstrated to be able to ensure the amplification of their Raman emission by several orders of magnitude, which results in the significant enhancement of recognizability and identification of security holograms. Practical significance. The technologies for hologram protection proposed in this work are based on the combination of different types of markings such as hidden holographic images, magneto-optical and fluorescent images of MPs, and Raman spectra of molecular structures that are enhanced by plasmonic-resonant methods. These technologies significantly increase the reliability, security, and authenticity of the marking and its identification. The results of this study will help in forming the basic technical requirements for design of portable devices for the identification of security hologram markings.

Исследование структуры и электрических свойств нанокомпозитных пленок W-=SUB=-x-=/SUB=-Si-=SUB=-1-x-=/SUB=-

An experimental investigation of the structure and phase composition by X-ray, Raman, and ultrasoft X-ray emission spectroscopy, as well as the study of the electrical properties of WxSi(1-x) films used as sensitive elements of superconducting single-photon detectors (SNSPD), depending on the thickness in the range from 7 to 80 nm, was carried out, according to the results of which it was found that the W3Si phase is presumably formed in films 20 and 40 nm thick with a resistivity of 8.4 10-5 and 6.0 10-5 Ω cm, respectively, containing the WSi2, W5Si3, and SiO2 phases, as well as WOx and a small share of β-W. Films with a thickness of 7 nm have the highest resistivity of 18.0 10-5 Ω·cm and contain nanocrystals, WSi2, SiO2, as well as β-W, and an amorphous silicon phase. Films with a thickness of 80 nm (the resistivity is also 18.0 10-5 Ω·cm) predominantly contain WSi2, as well as W5Si3 and SiO2, and, presumably, the W3Si phase.

Highly enhanced field emission from vertically aligned carbon nanotubes grown on a patterned substrate via non-lithographic method

In the present work, a silicon substrate has been patterned with a gold thin film of thickness 15 nm using thermal evaporation , followed by growth of carbon nanotubes (CNTs) using thermal chemical vapor deposition . The effect of temperature on the growth of CNTs on Au patterned substrate is studied using Raman and Field emission scanning electron microscope (SEM). A significant change in the growth of the CNTs grown on Au film patterned substrate with temperature can be observed using SEM images. However, no significant change in the micro crystallinity of the films was observed. Field emission properties of vertically aligned carbon nanotubes, grown at different temperatures, on gold film patterned substrate has been investigated. For the non-patterned substrate, for the CNT film grown at 900 °C, the current density comes out to be 8.0 mA/cm 2 @ 4.8V/μm, which increases to 14.6 mA/cm 2 in the case of CNT film grown on gold patterned substrate. The observed enhancement of nearly 180% in current density for the patterned substrate as compared to non-patterned silicon substrate is primarily attributed to the reduced electric field screening. The reduced screening is realized with the help of COMSOL simulation, showing a significant enhancement in the local electric field near edges. • Use of novel non- Lithographic technique to pattern CNT films. • Effect of temperature on the Growth of vertically aligned CNTs on patterned substrate. • Nearly 180% enhancement in Field emission current density for CNTs grown over patterned substrate at 900 °C. • Simulation based verification of enhancement in the Field emission properties due to reduced screening.

Investigation of the structure and electrical properties of nanocomposite films W-=SUB=-x-=/SUB=-Si-=SUB=-1-x-=/SUB=-

An experimental investigation of the structure and phase composition by X-ray, Raman, and ultrasoft X-ray emission spectroscopy, as well as the study of the electrical properties of WxSi1-x films used as sensitive elements of superconducting single-photon detectors (SNSPD), depending on the thickness in the range from 7 to 80 nm, was carried out, according to the results of which it was found that the W3Si phase is presumably formed in films 20 and 40 nm thick with a resistivity of 8.4·10-5 and 6.0·10-5 Ω ·cm, respectively, containing the WSi2, W5Si3, and SiO2 phases, as well as WOx and a small share of β-W. Films with a thickness of 7 nm have the highest resistivity of 18.0·10-5 Ω ·cm and contain nanocrystals, WSi2, SiO2, as well as β-W, and an amorphous silicon phase. Films with a thickness of 80 nm (the resistivity is also 18.0·10-5 Ω ·cm) predominantly contain WSi2, as well as W5Si3 and SiO2, and, presumably, the W3Si phase. Keywords: Superconducting single-photon detector, phase composition, X-ray amorphous structure, WSi superconducting films, spectroscopy.

Understanding the Efficiency of Mn4+ Phosphors: Study of the Spinel Mg2Ti1–xMnxO4

We present a spectroscopic study of Mn-doped Mg2TiO4 as a function of pressure and temperature to check its viability as a red-emitting phosphor. The synthesis following a solid-state reaction route yields not only the formation of Mn4+ but also small traces of Mn3+. Although we show that Mn4+ photoluminescence is not appreciably affected by the presence of Mn3+, its local structure at the substituted Ti4+ host site causes a reduction of the Mn4+ pumping efficiency yielding a drastic quantum-yield reduction at room temperature. By combining Raman and time-resolved emission and excitation spectroscopies, we propose a model for explaining the puzzling nonradiative and inefficient pumping processes attained in this material. In addition, we unveil a structural phase transition above 14 GPa that worsens their photoluminescence capabilities. The decrease of emission intensity and lifetime with increasing temperature following different thermally activated de-excitation pathways is mostly related to relatively small activation energies and the electric–dipole transition mechanism associated with coupling to odd-parity vibrational modes. A thorough model based on the configurational energy level diagram to the A1g normal mode fairly accounts for the observed excitation and emission─the quantum yield─of this material.

Measurements and analysis of rotational temperatures obtained with Raman and optical emission spectroscopy in a nonequilibrium nitrogen plasma

Rotational temperature measurements of N2(B3Πg), N2(C3Πu) and obtained by optical emission spectroscopy (OES) are compared with previous gas temperature measurements obtained with Raman spectroscopy in a nonequilibrium recombining nitrogen plasma at atmospheric pressure. The plasma is produced in a state of thermal and chemical equilibrium at about 7000 K using an inductively coupled plasma torch. It is then forced out of chemical equilibrium by imposing rapid cooling through a water-cooled tube. The gas temperature measured by Raman spectroscopy is about 3200 K at the exit of the tube. The rotational temperatures of N2(B) and N2(C) measured with OES are found to be in good agreement with the gas temperature, but the rotational temperature of N2 +(B) is found to be significantly above the gas translational temperature. We propose that this higher rotational temperature is the result of N2 +(B) being formed by the charge exchange reaction between N2(A3Σu +) and N+. Kinetic and QSS simulations are performed to support this assumption and a rate constant for this reaction is proposed.

Integrated Molecular Optomechanics with Hybrid Dielectric-Metallic Resonators.

Molecular optomechanics describes surface-enhanced Raman scattering using the formalism of cavity optomechanics as a parametric coupling of the molecule’s vibrational modes to the plasmonic resonance. Most of the predicted applications require intense electric field hotspots but spectrally narrow resonances, out of reach of standard plasmonic resonances. The Fano lineshapes resulting from the hybridization of dielectric–plasmonic resonators with a broad-band plasmon and narrow-band cavity mode allow reaching strong Raman enhancement with high-Q resonances, paving the way for sideband resolved molecular optomechanics. We extend the molecular optomechanics formalism to describe hybrid dielectric–plasmonic resonators with multiple optical resonances and with both free-space and waveguide addressing. We demonstrate how the Raman enhancement depends on the complex response functions of the hybrid system, and we retrieve the expression of Raman enhancement as a product of pump enhancement and the local density of states. The model allows prediction of the Raman emission ratio into different output ports and enables demonstrating a fully integrated high-Q Raman resonator exploiting multiple cavity modes coupled to the same waveguide.